Fireproof shielded containers for radioactive materials



P. BLUM Sept. 9, 1969 FIREPROOF SHIELDED CONTAINERS FOR RADIOACTIVEMATERIALS Filed Oct. l1. 1965 United States Patent 3,466,662 FIREPROOFSHIELDED CONTAINERS FOR RADIOACTIVE MATERIALS Paul Blum,Saint-Genis-Laval, France, assgnor to Societe Lyonnaise de PlomberieIndustrielle, Lyon (Rhone), France, a joint-stock company of FranceFiled Oct. 11, 1965, Ser. No. 494,697 Claims priority, applicationFrance, Oct. 21, 1964, 4 ,242 Int. Cl. G21h 5/00 U.S. Cl. 250--106 4Claims ABSTRACT 0F THE DISCLSURE In a container for radio-activematerials, of the kind comprising an inner casing, a lead screen closelysurrounding this casing and an outer shell, as for instance of steel,there is left between the lead screen and the outer shell anintermediate space which is lled with plaster (hydrated calciumsulphate) to form a refractory protective heat-insulating and watercontaining layer. The cover of the container may also comprise a layerof plaster between its lead screen and its outer plate.

This invention refers to containers for radioactive materials.

Radioactive materials are generally stored and transported withincontainers so arranged as to protect against dangerous radiations. Forthis purpose the casing in which the material is disposed, is generallysurrounded by a thick lead screen which is itself re-inforced by anouter metallic shell. But the devices or casks thus realized may bedamaged by violet shocks or by tire and therefore they are generallyplaced within another protective casing made of wood or like relativelydeformable material and having an outer metallic covering.

These containers are relatively expensive, their decontamination isdifficult. When the radioactive material generates an important quantityof heat, the latter is not easily dissipated through the container wallsand therefore the inner temperature rises undesrably.

The present invention has for its object to provide a container forradio-active materials which will not suffer from the aboveinconveniences.

In accordance with the present invention a container for radioactivematerials comprises an inner casing, a thick lead screen surrounding thesaid casing in direct contact therewith, an outer shell surrounding thelead screen, but of such dimensions as to leave an intermediate space,and a mass of plaster, i.e., hydrated calcium sulphate (SO4Ca, 11H20)poured into the said intermediate space to lill the same.

When the calcium sulphate sets, its volume increases and its mass istherefore applied under a considerable pressure against the lead screenand against the outer shell. There is thus obtained an eflicient bondingbetween the shell and the screen. This increases the mechanical strengthof the container and improves heat conductivity.

It is to be noted that the mechanical and the thermal characteristics ofthe mass which tills the intermediate space may be varied at will byincorporating to the calcium sulphate appropriate llers. In the case ofcontainers of small dimensions in which the heat generated by theradioactive material is negligible, the llers are preferably ofheat-insulating character. With containers of large dimensions in whichthe radioactive material may generate an important quantity of heat, itmay on the contrary be desirable to use heat-conducting llers. The

3,466,662 Patented Sept. 9, 1969 c ICC llers may besides improve themechanical characteristics of the calcium sulphate mass. Such is thecase for instance with llers of fibrous character, as for instance glasslibres, asbestos, wood libres, or the like. Vermiculite may be used withadvantage as a heat-insulating iiller, while metal chips or metallicpowders may increase heat conductivity.

The mass of hydrated calcium sulphate contains a considerable quantityof water. In the case of a re this water is liberated in the form ofsteam. In order to avoid bursting of the outer shell the latter ispreferably provided with vents which are normally closed by readilyfrangible covers or by easily fusible plugs. This generation of steamabsorbs a considerable quantity of heat, but even when the whole mass isfully dehydrated, it still forms an excellent heat insulating layer.

In the accompanying drawings:

FIG. 1 is a fragmental vertical section of a container according to thepresent invention.

FIGS. 2 and 3 are small scale views which diagrammatically illustratetwo steps during the manufacture of the container.

The container illustrated in FIG. l comprises an inner casing 1 ofconventional type, adapted to house the radioactive material to betransported. The upper end of this inner casing is closed by a removablecover 2, seals 3 being disposed below the underface of the cover and aflanged portion of the wall of the casing. A thick lead screen 4surrounds the inner casing 1 in direct contact with the outer surfacethereof. The cover 2 is provided with an upturned lateral edge and ithas also a thick lead layer or screen S on its upper face.

The upturned upper edge of the inner casing 1 is counected with an upperhorizontal flange 6 by an upwardly flaring frusto-conical intermediateannular portion 7, preferably made of stainless steel, which may bewelded to the said edge and to the flange. This intermediate portion iswide enough to provide a substantial space between the outer surface ofthe lead screen 4 and the flange 6. The flange 6 is itself welded to anouter metallic shell 8 of such dimensions as to leave an intermediatespace between its inner surface and the outer surface of the lead screen4. The outer edge of the cover 2 is similarly connected with an outerhorizontal flange 9 by an intermediate frusto-conical portion 10 made ofstainless steel, the said ange 9 being welded with an upper plate 11spaced from the upper surface of the lead layer or screen S.

The anges 6 and 9 of the container and of its cover are assembled bymeans of screws 12.

The intermediate space comprised -between the lead screen 4 and theouter shell 8 is lled with a mass 13 of hydrated calcium sulphateI(plaster) which has -been obtained by pouring this substance into thesaid space in the liquid or semi-liquid state. Also the space betweenthe lead layer 5 and the upper plate 11 is similarlyjilled with anothermass 13 of hydrated calcium sulphate. These masses 13, 13' connstitute alire-proof layer which protects the lead screens 4 and 5 and theystrongly bond the outer walls of the container, i.e., the shell 8 andthe plate 11, with the said screens. Further owing to the large quantityof water which they contain, they may absorb a considerable quantity ofheat at a relatively moderate temperature. In order to permit freeexhaust of the steam which would then be generated within the hydratedsulphate, the ilanges 6 and 9 are provided with appropriate passages orvents which are normally obturated by fusible plugs such as 14 and 15.The outer shell 8 may further comprise easily fragnible portions orfusible discs, such as 16.

FIGS. 2 and 3 illustrate the manufacturing step of a container accordingto the present invention. As shown in FIG. 2 the inner casing 1, madefor instance of stainless sheet-iron, is disposed in the invertedposition on an appropriate supporting surface, not illustrated. Atubular open-ended mould 17 is then placed on the casing with itsintumed lower edge resting on the intermediate frustoconical portion 7of the casing. Molten lead is poured linto the inner space A of themould to form the lead screen around the casing. When the lead issolidified, the mold is removed and the screen thus obtained is machinedto the exact configuration desired.

The outer shell 8 has been prepared separately with apertures such as 8ain its bottom. It is disposed at the inverted position on the unitformed by the inner casing and the lead screen, and the horizontalflange 6 is welded to the intermediate portion 7 and to the edge of theopen end of the outer shell 8. Alternatively this flange could have beenpreviously welded to the intermediate portion 7 before casting the leadscreen, if desired. In any case this horizontal flange 6 acts as acentering means for the outer shell 8 with respect to the innercasing 1. A liquid `or semi-liquid mass of hydrated calcium sulphate, ormore evactly of anhydrous calcium sulphate mixed with water, is thenpoured into the intermediate space B delimited by the outer surface ofthe lead screen 4, the intermediate annular portion 7, the horizontalflange 6 and the outer shell 8. When this mass has set, the apertures 8aare closed by means of fusible discs such as 16 (FIG. l).

The cover of the container is prepared in the same manner, but here theupturned lateral edge of the cover forms the mould into which the moltenlead is poured to form the layer or screen 5. The upper plate 11 isformed with apertures, not shown, through which the mass of calciumsulphate may be poured after the plate is welded to the outer fiange 9.As in the case of the apertures 8a of the outer shell 8, these aperturesof the upperplate are thereafter closed by fusible discs.

I claim:

1. In an open-ended container for radioactive materials comprising aninner casing, a protective lead screen surrounding said inner casing indirect contact therewith,

an outer shell surrounding said screen, and flange means to connect saidouter shell with said inner casing, the improvement in which said outershell is spaced from said screen to define therewith an intermediatespace, said container further comprising a solid non-shielding mass ofhydrated calcium sulphate filling said intermediate space to form aheat-absorbing barrier protecting said screen against fires.

2. In a container as claimed in claim 1, further having a cover to closeits upper end with said cover having an inner plate with an inner sideand an outer side, a protective lead layer in contact with the outerside of said plate, an outer plate to cover said lead layer, and flangemeans to connect said inner plate with said outer plate, the improvementin which said outer plate is spaced from said screen layer to definetherewith an intermediate space, said cover further comprising a solidnon-shielding mass of hydrated calcium sulphate filling saidintermediate space between said inner and outer plates to form aheat-absorbing barrier protecting said lead layer against fires.

3. In a container as claimed in claim 1, vent means on said outer shellto permit exhaust of steam from said solid -mass of hydrated calciumsulphate.

4. In a container as claimed in claim 2, vent means on said outer plateto permit exhaust of steam from said solid layer of hydrated calciumsulphate.

References Cited UNITED STATES PATENTS 3,005,105 10/1961 Lusk Z50-106 X3,111,586 11/1963 Rogers Z50-106 X 3,113,215 12/1963 Allen 250--106 X3,173,884 3/1965 Jackson Z50-108 X RALPH G. NILSON, Primary Examiner A.B. CROFT, Assistant Examiner U.S. Cl. X.R. 220-9; Z50-108

